Pending patent applications assigned to the assignee of this application and bearing Ser. No. 285,942 now U.S. Pat. No. 4,441,021 and Ser. No. 286,186 now U.S. Pat. No. 4,373,384 disclose a diesel-engine-timing meter for use in analyzing the timing of a diesel engine. Such analysis includes determining so-called timing angle; that is, the number of degrees between the time a piston in a selected cylinder reaches its top-dead-center position and the time that combustion takes place in that cylinder. Automobile manufacturers commonly specify the number of degrees at a specific engine speed as a compromise to numerous considerations which must be taken into account. Thus, a diesel-engine-timing meter determines the number of degrees between top dead center and combustion.
Top dead center is identified in the following manner. A diesel engine includes a wheel mounted on the end of the engine crankshaft so as to rotate therewith. A notch or other marking means is located in the periphery of the wheel. A receptacle for a magnetic probe is positioned on the engine block and is so located that the notch on the rotating wheel will pass the receptacle a known number of degrees of crankshaft rotation after the number one, or other selected cylinder has reached its top-dead-center position.
As described in the aforementioned applications, the combustion event is sensed by light occurring during combustion. The glow plug for the prechamber associated with the number one, or other selected, cylinder is removed and a luminosity probe is inserted in its place. The luminosity probe includes a sensor which responds to light produced during combustion and generates an electrical signal.
It is important that the reading on the timing meter be accurate. For example, if the meter reads "20.degree.", then there must in fact be a delay of 20.degree.. After determining precisely the magnitude of timing angle, the meter can be adjusted so that the displayed value is accurate.
One calibrator currently in the marketplace includes a loop at which a series of first pulses is generated, and a jack at which a series of second pulses is generated. The calibrator has means to establish the angle or delay between corresponding first and second pulses. The calibrator also has another selector for establishing the frequency of the pulses. In addition, such calibrator has other features not pertinent to the present discussion such as a knob to select the number of cylinders in the engine, a digital meter that displays timing angle when calibrating a timing light, etc.
Such calibrator is used to calibrate a spark-ignited-engine-timing meter by applying the first pulses to a clip which is normally applied to the conductor associated with a selected spark plug. The series of second pulses is applied to a magnetic probe which in use is mounted on the engine block to sense a notch or the like in the flywheel.